NEWS ARCHIVE

# THERMOMETER OR BAROMETER?

A well-known joke about a naive man who did not dare to take a bath under the following unusual reason:

I slipped into the tub barometer, and he showed the storm... it is Dangerous to swim!

But do not think that it is always easy to distinguish the thermometer from the barometer. There are thermometers, loyal, thermoscopes, who with no less right could be called barometers, and Vice versa. An example would be the old thermoscope invented by Heron of Alexandria.

The Thermoscope Gerona.

When the sun's rays pregreat balloon, the air in the upper part of the ball, extending, pressure on water and expels it through a curved tube to the outside; the water begins to drip from the end of the tube into the funnel, whence flows into the bottom drawer. In the same cold weather, on the contrary, the elasticity of the air in the balloon decreases and the water from the bottom drawer is displaced by the pressure of external air in a straight tube into a ball.

However, this device is sensitive to changes in barometric pressure: when the external pressure is weakened, the air inside the ball, kept still higher pressure, expands and displaces some of the water through the tube into the funnel; when increasing the external pressure of the water out of the drawer whoneeds into a ball due to the higher pressure outside. Each degree of temperature difference will cause the same change in volume of the air inside the balloon, as 760/273=about 2.5 mm difference in height of the barometric column (mercury). In Moscow barometric fluctuations reach more than 20 mm; this corresponds to 8°C in the thermoscope Gerona, it means that such a fall in atmospheric pressure can easily be taken for a rise in temperature of 8 degrees!

You see that old thermoscope not least is baroscope. One time there had us water barometers, which was in the same degree and thermometers; this, however, is not suspected not only buyers, but, it seems, and their inventor.

Entertaining physics J. Perelman

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